One of the first command you can use is SHOW DATABASES;
This command is used to show the current databases on the server.
If this is the first time anyone logged into MariaDB then you probably get the following output:

This 3 databases has already been created for you.
The next thing you will want to do is to create your own database, for this you should run CREATE DATABASE <database_name>;
So for example lets say we want to create the first db with the name firstDB.
We should just run: